Syntax

Parameters

A handle to a DxgkDdiAddDevice context block that is associated with a display adapter. The display miniport driver's function previously provided this handle to the DirectX graphics kernel subsystem.

*BacklightInfo

A value of type DXGK_BACKLIGHT_INFO that provides the current absolute level of backlight reduction.

Return Value

Returns STATUS_SUCCESS if it succeeds. Otherwise, it returns one of the error codes that are defined in Ntstatus.h.

Remarks

This function is mostly used for debugging and testing purposes to ensure a quality user experience with the display panel. The display miniport driver must always provide accurate information about the integrated display panel when this function is called.

Note that for some hardware a value of zero for BacklightInfo->BacklightUsersetting or BacklightInfo->BacklightEffective might not correspond to a Windows brightness level of zero percent. The operating system therefore requires absolute brightness information given by BacklightUsersetting and BacklightEffective. If the hardware uses brightness levels of 0 to 255, it must multiply those values by 256 to correctly map them to the 0 to 65535 range of BacklightUsersetting and BacklightEffective.

Computing backlight reduction ratio

The operating system assumes that, in response to a new brightness level request, the driver will boost pixel brightness by a factor of BacklightUsersetting / BacklightEffective = 1.0 / (1.0 - BRR).

As an example, if BRR = 0.2, the driver will typically boost brightness by a factor of 1.0 / (1.0 - BRR) = 1.25, so any pixel with a brightness value above 255 * (1.0 - BRR) = 204 will saturate. Using the value of BacklightInfo->GammaRamp provided by the driver, the operating system can more accurately estimate the distortion of pixel brightness for a particular image.